iOS: isMovingToParentViewController is not working

问题:

My setup is simple, and my issue is not very different from this one. However to better explain it I have posted it here:

NavController -> VC1 -> VC2

VC1 is root view controller of NavController. VC2 is accessible via Push segue from VC1.

I want to detect, within VC1, whether:

It appeared directly as root view controller (via Push) It appeared as a result of VC2 being popped

I read the docs which says following should tell me if later is true.

isMovingToParentViewController == NO 

However that is not the case, and above condition ALWAYS turns out to be TRUE. Which means that, (self.isMovingToParentViewController == NO) is always happening.

Here is my code:

- (void) viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    self.navigationController.navigationBarHidden = YES;

    //pushed to stack
    if (self.isMovingToParentViewController == YES)
    {
        //First time
      }
    else
    //popped off
    {
        //via Pop from VC2
    }    
}

Same is the case for viewDidAppear, too.

For a matter of fact check, I put breakpoint at the start, and checked that all of the following are FALSE, in both cases:

([self isMovingFromParentViewController])
([self isMovingToParentViewController])
([self isBeingPresented])
([self isBeingDismissed])

What is happening? Is there anything I goofed up in my storyboard? Please help...

回答1:

Unfortunately, isMovingToParentViewController isn't true for the root view controller, so I usually handle this situation with a BOOL,

@implementation ViewController {
    BOOL isFirstAppearance;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    isFirstAppearance = YES;
}

-(void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    if (isFirstAppearance) {
        NSLog(@"root view controller is moving to parent");
        isFirstAppearance = NO;
    }else{
        NSLog(@"root view controller, not moving to parent");
    }
}

回答2:

A simple solution is by adding a flag on viewWillDisappear setting it to YES if the VC1 has been disappeared. Else the view has never been disappeared so it is the first push (RootViewController of Navigation Controller).

Example Code

BOOL hasDisappeared;

-(void)viewWillAppear:(BOOL)animated
{
    if (hasDisappeared==YES) {
        //VC2 has been popped
    }
    else
    {
        //VC1 is the rootViewController
    }
}

-(void)viewWillDisappear:(BOOL)animated
{
    //Pushing to VC2
    hasDisappeared=YES;
}

回答3:

Since it appears that isMovingToParentViewController is only set when a viewController is being pushed to the navigation stack, and not set for the initial rootViewController, I'd suggest using the following:

 if([self.navigationController.viewControllers containsObject:self])
 {
     // being popped to self here
 }
 else
 {
     // being pushed here
 }